Flatten surface on inclination
In the linked file I can't see the same thing as you, but for example you have this artifact:

It's because you have ngons, face with more than 5 vertices, which tends to create artifacts, especially on non-flat surfaces (it stretches the triangles):

Here is a way to fix it, there might be a better but it's just to show you how to keep quads:

Also, you use crease and Bevel modifier, if you begin in modeling perhaps you should bevel &quot;manually&quot; instead, and avoid crease and Bevel modifier, they are tricks and you won't always be able to use them, but it's only my opinion...